Electron tube



Nov. 1, 1932. K. PoHLHAusEN ELECTRON TUBE Filed May 15. 1929 Patented Nov. 1, 1932 tJTE STATE PATENT OFFICE v KARL POHLHAUSEN, OF BERLIN-HALENSEE, GERMANY, ASSIGNOR TO SIEMENS- SCHUCKERTWERKE AKTIENGESELLSCHAFT, OF BERLIN-SIEMENSSTADT, GERIVIANY,

- A CORPORATION OF GERMANY ELECTRON TUBE Application filed May 15, 1929, Serial No. 363,157, and in Germany May 12, 1928.

My invention relates .to improvements in electron tubes, and more particularly in highpower electron or thermionic cathode tubes as used in the transmitting stations of radlo communication plants. g

One object of my invention is to protect the filament shaped thermionic cathode of the electron tube against mechanical stresses originating from electrostatic forces exerted upon said cathode. v

A further object of my invention consists in providing the electron tube with auxiliary electrodes the potential of which lies in the vicinity of the cathode potential (preferably agrees with the cathode potential) and wh ch are so located, that the electrostatic forces exerted on the cathode are reduced to a minimum.

A still further object of my invention is to provide a thermionic cathode tube with an anode cylinder within which the filament-like elementsof the cathode, which are substantially parallel to the axis of the anode cylinder, are located on an imaginary cylindrical surface concentric to the anode cylinder, rodshaped auxiliary electrodes parallel to the axis of the anode cylinder being provided, which are likewise located on an imaginary cylindrical surface enclosing the cylinder on which are located the filament elements.

These and other embodiments of my invention will be more fully described with reference to the accompanying drawing hereto.

, In which Figs. 1 and 2 represent transverse sections through the electrode structure of a thermionic tube, according to my invention, showing two forms in which the invention may be reduced to practice,

Fig. 3 is a diagrammatic representation of the arrangement of the electric connections between the several filament lengths, and

Fig. 4 represents the general arrangement of such an electrode structure, involving either of the foregoing modifications, in a thermionic tube.

Referring to Figs. 1 and 2, 1 is the cylindrical anode, in this case of hollow cylindrical form, which may be arranged in an evacuated Vessel 6 for instance as shown in Fig. 4c.

The thermionic cathode structure is disposed within this anode cylinder. The cathode itself consists of a plurality of filament lengths arranged physically substantially in parallel to one another. Electrically these lengths may be connected together in any approved manner, such as in series, for instance as shown in Fig. 3. These filament lengths are located between a number of rod shaped parallel auxiliary electrodes electrically connected to the filament cathode, so that they have substantially the same average potential as the filament with respect to the anode. They thus screen the several filament lengths against the electrostatic forces emanating from the anode. They may serve at the same time as supports for the filaments.

In the modification illustrated in Fig. 1 four rod-shaped auxiliary electrodes 3, having the same potential as the filaments, are located at'the corners of a square, while the four filaments 2 are arranged within this square symmetrically to the holders.

In the modification illustrated in Fig. 2 the individual filaments and rod-shaped auxiliary electrodes are arranged in concentric circles, the auxiliary electrodes being placed on the outer circle, two rods being always located in the vicinity of each filament length and symmetrically to it. The auxiliary electrodes again would possess substantially the potential of the heated filaments 2.

- From Fig. 2 it will be noted that the screening against the anode is much more effective than in Fig. 1. Thea'rrows "emanating in that figure from one of the filament lengths indicate the planes in which each filament length isscreened by several auxiliary electrodes which are located in each of the planes. Eachfilament length is thus arranged at the intersection of the shielding planes.

If the auxiliary electrodes serve in such arrangements at the same time as holdersfor the cathode one or more of these auxiliary electrodes may also be used as leading-in and leading-out wires for the heating current of the cathode as shown in Figs. 3 and i. The remaining auxiliary electrodes have then only screening function. In both cases'it is possible to arrange the leading-in orthe lead.

ing-out wire of the heating current on the same side of the electron tube.

In the following is given a formula in dicating how the individual filaments and rod-shaped auxiliary electrodes should be arranged and dimensioned, if we consider in Fig. 3the two outer filaments located in one plane between two auxiliary electrodes. In this example R represents the radius of the anode cylinder,

T is the radius of the filaments,

T the radius of the rod-shaped auxiliary electrodes, V

(i the distance of the auxiliary electrodes from the axis of the anode cylinder, and

(1 the distance of the filaments from the axis of the anode cylinder.

If now is chosen= 0.05, and 0.01,

an accurate calculation for %=O.7 gives as place for the filament free from electrostatic forces (L2 0.225. For g 0.5 results The arrangements described have inciden tally the advantage, that mutual the electrodynamic forces exerted by the heating current on the heated lengths are to a large extent equalized, if in accordance with Fig. 3 of the drawing the heated filaments are consecutively connected in series, so. that the field forces in the individual current loops very nearly compensate one another.

Various modifications and changes may be made without departing from the spirit and the scope of theinvention.

I claim as my invention:

1. An electron tube having an anode and a thermionic cathode mounted within said anode, said cathode consisting ofa plurality of substantially parallel filaments, and a plurality of mechanically resistive auxiliary electrodes mounted in parallel to said filaments and at the corners of a polygon which includes said filaments, some of the polygon sides including each at least one of the said filaments, whereby each of said filaments included in a polygon side is shielded by two of said electrodes ina direction co-planar with the polygon side against the electro-' static forces exerted by the anode.

2. An electron tube having an anode and a thermionic cathode mounted within said anode, said cathode consisting of a plurality of substantially parallel filaments, and a plurality of mechanically resistive auxiliary electrodes mounted in parallel to said filaments and at the corners of a regularpolygon, said filaments being disposed on at least two opposite sides of said polygon, whereby each of said filaments included in a polygon side is shielded by two of said electrodes in a direction co-planar with the polygon side against the electrostatic forces exerted by the anode.

3. An electron tube having an anode and a thermionic cathode mounted within said anode, said cathode consisting of a plurality of substantially parallel filaments, and a plurality'of mechanically resistive auxiliary electrodes mounted in parallel to said filaments and at the corners of a regular polygon, said filaments being disposed on a circle inscribed within the contour of said polygon, each filament being disposed in a plane through two auxiliary electrodes of said polygon, whereby each of said filaments included in such a plane is shielded in the direction of said plane by two auxiliary electrodes within said plane against the electrostatic forces exerted by the anode.

4. An electron tube having an anode and a thermionic cathode mounted within said anode, said cathode consisting of a plurality of substantially parallel filaments, and a plurality of mechanically resistive auxilary electrodes mounted in parallel to said filaments and at the corners of a regular polygon, said filaments being disposed on a circle inscribed within the contour of said polygon, each filament being disposed at the intersection of two planes through two pairs of auxiliary electrodes, whereby each filament is shielded in the directions of its pertaining planes by the pertaining electrodes against the electrostatic forces exerted by said anode.

In testimony whereof I affix my signature.

KARL POHLHAUSEN. 

